<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>

        * {
            box-sizing: border-box;
            -webkit-box-sizing: border-box;
            -moz-box-sizing: border-box;
        }

        div.simple {
            width: 500px;
            margin: 20px auto;
            background: red;
        }

        div.fancy {
            width: 500px;
            margin: 20px auto;
            padding: 50px;
            border-width: 10px;
            background: green;
        }
    </style>
</head>
<body>
<div class="simple">abc</div>
<div class="fancy">abc</div>
</body>
</html>